RUNX2 contains both polyQ and polyA stretches separated by a single glutamate residue, and this polyQ/polyA region is predicted to form a CC (Fig. 1G) that expands with polyA elongation up to 10–12 additional alanines (Fig. 3B) as observed in cleidocranial dysplasia patients (39,40). Here, RUNX2 is linked to cleidocranial dysplasia 1.